Driven by injection drug use, Kazakhstan and other Central Asian nations are currently experiencing the fastest growing HIV incidence in the world and continue to report huge gaps in the continuum of HIV care for PWID. According to 2014 national data, only one-third of the estimated 19,000 HIV-positive PWID in Kazakhstan are ever linked to HIV care and only 10% initiate ART with 4% achieving viral suppression. As Kazakhstan is expanding eligibility for ART from <350 CD4 to <500 CD4 in 2015, there is an urgency to enroll previously ineligible HIV-positive PWID in ART. Large gaps in Kazakhstan's continuum of care for PWID mirror gaps found in other countries in which only a small proportion of PWID initiate ART. Mounting research demonstrates that improving rates of ART among PWID may be an effective strategy to prevent HIV transmission, lower mortality, improve quality of life, and reduce drug and sexual risk behaviors. There is a critical need for effectiveness and implementation research to identify how best to improve HIV service delivery to close the critical Treat gap in the continuum of care. This will occur by identifying and linkng HIV-positive PWID to HIV care, and reaching out to those who have never been in HIV care, are intermittent users of care, or have dropped out of treatment. The proposed study is designed to evaluate the implementation and effectiveness of an enhanced HIV service integration package (BRIDGE) that may be scaled up in Kazakhstan's vast network of needle-syringe programs (NSPs) for PWID. This package includes low threshold strategies of peer-driven recruitment, HIV counseling and rapid testing (HCT) in NSPs conducted by HIV care clinic nurses, and ARTAS, CDC's highly effective case management strategies for linking PWID to HIV care. BRIDGE is systematically designed to address specific service barriers to testing PWID for HIV, linking them to HIV care, and promoting ART initiation. This study will employ an innovative stepped wedge design to evaluate implementation and effectiveness of BRIDGE on improving linkage to HIV care and initiation of ART in 24 NSPs located in 4 geographically disparate Kazakhstani cities using site-level data collected from NSPs and HIV clinics. We will also conduct a longitudinal panel study with a random sample of HIV-positive PWID (N=600) from four cities in Kazakhstan using repeated assessments at baseline, 6-, and 12-months follow-up. This study will employ mixed methods to identify multi-level structural, community, and organizational factors that influence the implementation and effectiveness of BRIDGE and the cost of BRIDGE, examining implications for cost-effectiveness, feasibility of expansion, and sustainability. The study builds on the investigative team's extensive HIV intervention research among PWID in Kazakhstan in collaboration with the Republican AIDS Center over the past decade. It addresses implementation research questions to improve and integrate HIV service delivery systems for PWID that are not only important to the region, but have relevance to other countries that have concurrent injection drug use and HIV epidemics.